It is known that lithium-containing drugs are effective in feeling stabilization and anti-depression, so that they are used widely as feeling-stabilizer and antidepressant drugs. Tablets of lithium carbonate (for oral administration) are generally prescribed as a feeling stabilizer as well as a drug for bipolar disorder (circulatory psychosis) or anti-depressive drug.
However, when such lithium-containing drug is administrated to patients, it is necessary to control or adjust the concentration of lithium in serum within a proper range. In fact, the lithium carbonate (Li2CO3) has such a characteristic that its administration effect is exhibited only when the concentration of lithium in blood arrives at nearly a “lithium poisoning level”. In other words, when the drug is administrated, the therapeutic drug monitoring (TDM) is indispensable so as to monitor the lithium concentration in blood, since a therapeutic range is very near to the poison level.
In practice, it is necessary to control or limit the concentration of lithium in a patient blood sample within a limited range of generally from 0.6 to 1.2 mEq/L. In fact, when the lithium concentration in serum is lower than 0.6 mEq/L, no anti-depressive effect is expected. On the contrary, excess administration over 1.5 mEq/L of the concentration in plasma will result in the lithium poisoning. Overdose result in a fatal cause of symptoms of poisoning including tremor, alalia, nystagmus, renal disturbance and convulsion. Therefore, when a sign of latently dangerous symptoms of lithium-poisoning is observed, treatment with such lithium-containing drug must be stopped and the concentration in plasma must be re-measured so as to take a necessary measurement and to ease the lithium-poisoning.
Thus, the lithium salt is an effective medicine in the treatment of depressive patients, but overdose result in serious troubles. Therefore, when a lithium-containing anti-depressive drug is administered, it is indispensable to monitor the concentration of lithium in serum and to assure that the concentration is always kept with a limited range of from 0.6 to 1.2 mEq/L. Therefore, the quantitative measurement of lithium in serum is necessary in the treatment of depression patient.
Several liquid reagent compositions that permit colorimetric determination of lithium for the clinical laboratory test have been developed.    Patent Document 1 discloses a reagent composition used to measure the concentration of lithium in a biological sample by using primary color body cryptideinofa.    Patent Document 2 discloses an analytical reagent which reacts with lithium ion, comprising a macrocyclic compound having a pyrrole ring and eight bromine (Br) atoms combined at β position of the pyrrole ring.    Non-Patent Document 1 discloses that lithium ion can be detected by a compound in which all hydrogen bonded to carbons of tetraphenylporphyrin are replaced by fluorine.